As a hierarchical structure display device which changes its display content on a display screen in a hierarchical fashion, hierarchical structure display devices disclosed in Japanese Patent Application Laid-open No. Hei 5-182090 and Japanese Patent Application Laid-open No. 2005-10451 are known. In the display device disclosed in Japanese Patent Application Laid-open No. Hei 5-182090, two vertical cursor keys (switches) and four selection function keys (switches) are provided outside a display screen to switch a screen display.
As is understood from the above description, the display device disclosed in Japanese Patent Application Laid-open No. Hei 5-182090 includes a large number of switches. Therefore, switching to a different mode can be easily selected in a cyclic manner within a basic mode. Moreover, even after the switching to the different mode, the switching selection can be cyclically made with ease in the different mode after the switching.
On the other hand, in contrast to the above-mentioned example, the display device disclosed in Japanese Patent Application Laid-open No. 2005-10451 is provided with only one switch. The display device disclosed in Japanese Patent Application Laid-open No. 2005-10451 uses a switch-ON duration time to select the switching to a different mode in a cyclical manner within the basic mode or to perform the switching selection in a cyclical manner within the different mode after the switching.
The use of the switch-ON duration time will be described briefly. For example, a control unit of the display device determines whether or not the switch-ON duration time is five seconds or longer. Then, when it is determined that the switch-ON duration time is five seconds or longer, the display is switched to be in the different mode. When it is determined that the switch-ON duration time is shorter than five seconds, the display is switched to that for the next switching selection in the same mode.
In the case of the display device disclosed in Japanese Patent Application Laid-open No. 2005-10451, if an operator is not informed of a precise processing status of a switch operation, the display is switched to be in the different mode against the will, for example. Therefore, the display device enables the operator to recognize the execution of the switch operation and a remaining time before the switching to the different mode (to recognize the processing status of the switch operation).